There have been often used a QFP (Quad Flat Package)-type and a BGA (Ball Grid Allay)-type CSP (Chip Size Package/Chip Scale Package) semiconductor device, so as to (i) meet a recent tendency toward reduction of electronic devices in size and (ii) to conform to automation of an assembly process. Particularly, to meet high-speed and high-performance signal processing of a semiconductor chip in the semiconductor device, a demand for more external connection terminals has been increasing. Therefore, there has been often employed the BGA-type semiconductor device in which the external connection terminals are arranged in two-dimensional manner at the bottom of the semiconductor device.
FIG. 8 shows a cross-sectional configuration of a BGA-type CSP semiconductor device 110, and a lower part of FIG. 8 also shows a defective condition that occurs in the semiconductor device 110 which will be described later.
In the semiconductor device 110, a semiconductor chip 103 is mounted on a semiconductor chip mounted region 102 that is on an upper surface of a wiring board 101, and an electrode pad section of the semiconductor chip 103 is electrically connected to a wire bonding terminal section of the wiring board 101 through a thin metallic wire (wire) 107. Further, the semiconductor chip 103 and the thin metallic wire 107 are sealed with a resin 108 so as to be cover with the resin. Furthermore, a metallic external connection terminal 109 such as a solder ball is provided on a lower surface of the wiring board 101. A package structure of the semiconductor device 110 as described above is a dominating structure of a BGA-type package these days, and is more advantageous in terms of size reduction and electrical properties, as compared to other semiconductor package structures. Therefore, the package structure is often employed in portable electronic devices such as mobile phones and portable video game machines.
In order to form the external connection terminal 109 at the time of manufacturing the above-mentioned semiconductor device 110, the following method is often employed: a solder used for the external connection terminal 109 is melted by a heating device such as a reflow oven. Further, in order to mount the semiconductor device 110 on a mount substrate, the following method is generally employed: solder paste or flux is applied to the mount substrate; the semiconductor device 110 is mounted on the solder paste or the flux; and the solder ball that is the external connection terminal 109 is melted by the heating device. As such, the external connection terminal 109 is connected to the mount substrate.
Regarding the solder ball constituting the external connection terminal 109, a material of the solder ball has been recently shifted from a eutectic solder to an unleaded solder with consideration to the environment. The unleaded solder has a higher melting point than the eutectic solder. Therefore, heating temperature tends to increase in a reflow process at the time of manufacturing the semiconductor device 110 as described above, at the time of mounting the semiconductor device 110 on the mount substrate as described above and the like times. Specifically, the heating temperature tends to increase by the order of 20° C. to 30° C.
In this manner, as the heating temperature increases in the reflow process, the following phenomenon occurs. That is, the heat causes the semiconductor device 110 to suffer from vaporization and expansion of moisture that is absorbed into the semiconductor device 110, thereby causing deformation of an outside shape of the semiconductor device 110. As a result, there occur such problems that (i) the semiconductor device 110 becomes faulty or becomes impossible to be mounted, and (ii) a wire of the semiconductor device 110 is broken (see the lower part of FIG. 8).
More specifically, the above-mentioned semiconductor device 110 is manufactured by mounting a semiconductor chip on a wiring board, subjecting to wire bonding, and sealing the semiconductor chip and the wire with a resin. In such a semiconductor device 110, moisture that is absorbed after assembly of the semiconductor device tends to collect in the vicinity of interfaces between components of the semiconductor device 110, mainly in a contact section between the semiconductor chip and the wiring board. Particularly, a lot of moisture tends to collect in an interface (that is, the semiconductor chip mounted region 102 of the semiconductor device 110) between the semiconductor chip and the wiring board. The moisture is vaporized and expanded by the heat applied in the reflow process. This particularly causes great expansion of the semiconductor chip mounted region of the wiring board. As a result, the above-mentioned problems such as deformation of the outside shape occur. Such problems tend to occur more often in a semiconductor device that employs a thin wiring board.
In order to solve the problems, in a semiconductor device that has a configuration in which a semiconductor chip is bonded to a wiring board by a sheet-like adhesive, the following method is employed to increase adhesiveness of the semiconductor chip to the wiring board: a solder resist is applied in layers to the wiring board so as to reduce influence caused by unevenness of a wiring pattern that is provided under the solder resist. Further, in order to solve the problems, the following method is also employed: a through hole is provided in a part of the semiconductor chip mounted region of the wiring board so that moisture that collects within the semiconductor device can be discharged (see Patent Literature 1).
FIG. 9 shows a cross-sectional configuration of a semiconductor device 110a, which is the semiconductor device 110 which employs the method of providing the through hole so that collected moisture is discharged from the through hole. A lower part of FIG. 9 shows a defective condition (problem) that occurs in the semiconductor device 110a, which will be described later. As shown in FIG. 9, in the semiconductor device 110a, a through hole 111 is provided in the wiring board 101 of the semiconductor chip mounted region 102 so that the collected moisture is discharged from the through hole 111.
However, in the method of applying the solder resist in layers to the wiring board to reduce the influence caused by the unevenness of the wiring pattern that is provided under the solder resist, a solder resist needs to be applied several times in a process for manufacturing the wiring board. This causes problems such as increase in manufacturing processes and increase in cost of manufacturing. Further, in the method of providing the through hole in a part of the wiring board so that moisture that collects within the semiconductor device can be discharged, it is impossible to discharge all the collected moisture. Therefore, expansion occurs in a region where moisture is left, that is, in a region other than the part where the through hole is provided in the semiconductor chip mounted region.    Patent Literature 1    Japanese Patent Application Publication,    Tokukai No. 2001-15628 A (Publication Date: Jan. 19, 2001)